Cardiotonic agents such as substituted 4,5-dihydro-6-[4-(1H-imidazol-1-yl)phenyl]-3(2H)-pyridazinones and 6-[4-(1H-imidazol-1-yl)phenyl]-3(2H)-pyridazinones are described in U.S. Pat. No. 4,353,905.
Antihypertensive agents which have been found to possess differing affinities at adenosine receptors are N.sup.6 -(1- and 2-benzocycloalkyl)adenosines described in U.S. Pat. No. 4,501,735.
Combinations of the above noted cardiotonic agents and selected antihypertensive agents which attribute their activity to inhibition of angiotensin-converting enzyme (ACE inhibitors) are described in U.S. Ser. No. 612,275 filed May 21, 1984, now U.S. Pat. No. 4,584,299. Other combinations of antihypertensive agents and diuretics are well-known in the art. ACE-inhibiting antihypertensive agents have also been reported to be useful in combination with diuretics, saluretics, .alpha.-adrenolytic, .beta.-blockers, calcium antagonists or vascular dopaminergic receptor agonists. See European Patent Publications 51,020, 69,846, and 49,658.
The present invention relates to a combination of selected cardiotonic agents with selected adenosine receptor agonist antihypertensive agents resulting in a synergistic increase in myocardial contractility and cardiac output thereby rendering such combinations useful in treating heart failure.